Method and apparatus for needle placement and entry point determination in percutaneous procedures

ABSTRACT

A method for determining the best entry point for a percutaneous procedure, such as with a biopsy needle, comprises selecting first and second arbitrary entry points on a patient; determining the three dimensional (3-D) orientation of the needle at the first arbitrary entry point for pointing the needle at the primary target; determining the 3-D orientation of the needle at the first arbitrary entry point for pointing the needle at the secondary target; determining the 3-D dimensional orientation of the needle at the second arbitrary entry point for pointing the needle at the primary target; determining the 3-D orientation of the needle at the second arbitrary entry point for pointing the needle at the secondary target; determining a 3-D line representing the intersection of a first plane containing the first arbitrary entry point, the primary target point, and the secondary target point, and a second plane containing the second arbitrary entry point, the primary target, and the secondary target point, whereby the 3-D line provides a position and orientation for the needle for performing needle biopsy of the primary target through the secondary target.

This application is a divisional application of Ser. No. 09/883,422,filed Jun. 18, 2001 now abandoned.

The present invention relates to the field of percutaneous proceduresand, more specifically, to method and apparatus for needle placement,such as for needle biopsy, and for determining an appropriate entrypoint for such a needle.

Reference is hereby made to copending Provisional Application No.60/212,199 filed on Jun. 16, 2000 in the names of Benedicte Bascle,Nassir Navab, and Bernhard Geiger and entitled “METHOD FOR NEEDLEPLACEMENT IN A FIXED NUMBER OF ITERATIONS USING PERSPECTIVE INVARIANTSAND METHOD FOR DETERMINING THE BEST ENTRY POINT FOR PERCUTANEOUSPROCEDURES”, whereof the disclosure is herein incorporated by reference.

Reference is also herein made to the following documents whereof thedisclosure is herein incorporated by reference: U.S. Pat. No. 6,028,912“APPARATUS AND METHOD FOR POINT RECONSTRUCTION AND METRIC MEASUREMENT ONRADIOGRAPHIC IMAGES”; U.S. Pat. No. 5,930,329 “APPARATUS AND METHOD FORDETECTION AND LOCALIZATION OF A BIOPSY NEEDLE OR SIMILAR SURGICAL TOOLIN A RADIOGRAPHIC IMAGE”; and U.S. patent application Ser. No.09/408,929, entitled “METHOD AND APPARATUS FOR VISUAL SERVOING OF ALINEAR APPARATUS” and filed on 30 Sep. 1999 in the name of inventorBenedicte Bascle.

In accordance with an aspect of the present invention, a method isprovided for determining the best entry point for percutaneousprocedures, given a primary target for the biopsy and a secondary targetthrough which the needle must pass on its way to the primary target.

In accordance with another aspect of the invention, a method is providedfor positioning a biopsy needle from a given entry point to a giventarget.

In accordance with another aspect of the invention, a method is providedfor visual servoing of a needle in a plane in a fixed number ofiterations.

In accordance with an aspect of the present inventive concepts, it isherein shown how precise 3D-alignment of a tool from a fixed entry pointto a target can be achieved by performing visual servoing of the tool in3 successive planes using two different views. Visual servoing of theneedle or tool in each plane is achieved using a technique based onprojective invariants. 3D alignment is obtained in exactly twelveiterations using the technique. If there are multiple (n) targets, theapproach does not require n*12 iterations, but 6*(n+1).

In accordance with another aspect of the present inventive concepts, amethod for finding the entry point to reach a given target while passingthrough a secondary target is herein described.

The invention will be more fully understood from the following detaileddescription, in conjunction with the Drawing, in which

FIG. 1 shows needle placement by visual servoing in 3 successive planesusing 2 views;

FIG. 2 shows visual servoing of a needle in a plane using cross-ratios;

FIG. 3 shows needle orientation from fixed point F to multiple targets;

FIG. 4 shows a best entry point to reach one target by passing through asecondary target;

FIG. 5 shows a flow diagram or chart of a method in accordance with theinvention for determining the best entry point for percutaneousprocedures, given a primary target for the beiopsy and a secondarytarget through which the needle must pass on its way to the primarytarget;

FIG. 6 shows a flow diagram or chart of a method in accordance with theinvention for positioning a biopsy needle from a given entry point to agiven target; and

FIG. 7 shows a flow diagram or chart of a method in accordance with theinvention for visual servoing of a needle in a plane in a fixed numberof iterations.

With regard to needle placement by visual servoing in 3 successiveplanes, using 2 views, reference is made to copending U.S. patentapplication Ser. No. 08/722,725, entitled “APPARATUS AND METHOD FORPOSITIONING A BIOPSY NEEDLE” and filed 30 Sep. 1996 in the name ofinventors Nassir Navab and Bernhard Geiger, whereof the disclosure isherein incorporated by reference.

Reference now is made to FIG. 1.

For illustrative purposes, it is assumed that imaging is provided by asimple uniplanar X-ray fluoroscope (C-arm) or any other imaging modalitywhose imaging process can be modeled by a pinhole camera model. Theneedle itself is manipulated by a mechanical device such as a passive oractive robotic arm that allows arbitrary pivoting of the needle aroundits tip. The operator, physician, surgeon or doctor, chooses a fixedneedle entry point F on the patient, and places the needle device in away that its needle tip is located at that entry point. No calibrationof the set-up or registration of the patient to the set-up is required.

The C-arm is then positioned, so that the target area and a part of theneedle are both visible on the X-ray image I₁. The surgeon defines theprojection f of the needle entry pointy F and projection t of the 3Danatomical target T in the image. At this point of the description, itis assumed T remains static during the procedure.

First, the mechanical device moves the needle in an arbitrary plane P₁containing F until the projection of the needle is aligned with thetarget t in the image I₁ (see FIG. 1 a). This can be performed in 3iterations using the visual servoing technique presented in the nextsection. The final position of the needle in plane P.sub. 1 is calledD₁.

The system repeats this process by choosing a second plane P₂ containingF. The choice of P₂ is arbitrary. In practice, the system takes P₂perpendicular to P₁ for precision purposes. The needle is rotated inplane P₂ until it is visually aligned to the target t in the image I₁(see FIG. 1 b). This is done as previously described by using the visualservoing technique presented in section 2. The position of the needlethat gives visual alignment is called D₂.

The positions of the needle D₁⊂P₁ and D₂⊂P₂ define a unique plane P,which contains the X-ray source, the target point T and the fixed entrypoint F. This is essentially the maximum information that can beobtained from a single viewpoint.

The physician needs to move the C-arm to a second viewing direction. Thesurgeon defines projection f′ of needle entry point F and the projectiont′ of the 3D target point T in the new image I₂. Next, the needle ismoved only in the plane P until the needle is once again visuallyaligned to the target in the image I₂ (see FIG. 1 c). This is done usingthe visual servoing approach of section 2. This results in the final 3Dalignment D_(t) of the needle, the entry point and the anatomic targetpoint. The needle is then ready to be inserted. The correctness of thealignment can also be checked by moving the C-arm to a third viewingdirection.

Visual Servoing of a Needle in a Plane Using Cross-ratios

With regard to visual servoing of a needle in a plane usingcross-ratios, reference is made to the afore-mentioned U.S. patentapplication Ser. No. 09/408,929, entitled “METHOD AND APPARATUS FORVISUAL SERVOING OF A LINEAR APPARATUS”.

Reference now is made to FIG. 2.

In the previous section, it was shown how 3D alignment of a needle to atarget can be achieved by performing visual servoing of the needle inthree successive planes. There now follows an explanation of how thevisual servoing of the needle in a plane is performed. This is a newtechnique based on projective invariants and is described as follows:

Let Π be the plane in which the needle is rotated, and F the fixed pointaround which the rotation is done. The initial orientation L₁ of theneedle in plane Π is arbitrary. T is the 3D target point.

An image I is taken of the scene. The 3D position L₁ of the needleprojects onto line l₁ in the image. The position of l₁ is detected andstored in memory.

The needle is rotated in plane Π around fixed point F by an arbitraryamount θ₁. This brings it to position L₂. Another image is taken. The 3Dline L₂ projects onto 2D line l₂ in the image. The position of l₂ isdetected and stored in memory.

The needle is rotated again by an angle θ₂. This puts it into positionL₃. Another image is obtained. L₃ projects onto l₃ in the image. l₃ isdetected and its position stored in memory.

The intersection point of l₁, l₂ and l₃, denoted f, is determined byleast squares. Note that f is the projection of the fixed point F aroundwhich the needle is rotated.

Let t be the projection of the 3D target T in the image. We assume tremains static during the procedure. The position of t is giveninteractively by the surgeon.

The line l_(t)=(ft) is constructed. Note that l_(t) is the 2D projectionof the 3D position L_(t) of the needle that achieves visual servoing(e.g. the visual alignment of the needle and the target) and that wewish to estimate.

l₁, l₂, l₃ and l_(t) form a pencil of 2D lines. The cross-ratio c=(l₁,l₂, l₃, l_(t)) of these lines is calculated. This is done using anarbitrary line m that intersects all four lines. If q₁=l₁∩m, q₂=l₂∩m,q₃=l₃∩m and q_(t)=l_(t)∩m are the intersections of l₁, l₂, l₃, l_(t)with m, then

$\begin{matrix}{c = {\left( {l_{1},l_{2},l_{3},l_{t}} \right) = \left( {q_{1},q_{2},q_{3},q_{t}} \right)}} \\{= {\left( {q_{1}q_{3}*q_{2}q_{t}} \right) \div \left( {q_{1}q_{t}*q_{2}q_{3}} \right)}}\end{matrix}.$Note that the value of c is invariant to the choice of the line m.

Cross-ratios are one of the invariants of projective geometry. Thereforethe cross-ratio of a pencil of 3D lines is equal to the cross-ratio ofthe pencil of 2D lines formed by its perspective projections in animage. Therefore the cross-ratio (L₁, L₂, L₃, L_(t)) of the four 3Dlines L₁, L₂, L₃ and L_(t) is equal to c, e.g. (L₁, L₂, L₃, L_(t))=(l₁,l₂, l₃, l_(t))=c.

From (L₁, L₂, L₃, L_(t)), we estimate the angle θ_(t) necessary torotate the needle from position L₃ to L_(t). The formula for θ_(t) comesfrom the relationship between the cross-ratio of four lines and theangle between these lines. This gives:

$\left( {L_{1},L_{2},L_{3},L_{t}} \right) = {\frac{\left( {{\sin\left( {\theta_{1} + \theta_{2}} \right)}*{\sin\left( {\theta_{2} + \theta_{t}} \right)}} \right)}{\left( {{\sin\left( {\theta_{1} + \theta_{2} + \theta_{t}} \right)}*\sin\;\theta_{2}} \right)}.}$Using the fact that (L₁, L₂, L₃, L_(t))=c, the equation can be rewrittenas follows:

${{\left( {c - 1} \right)\sin\;\theta_{2}\cos\;\theta_{t}} + {\left( {\frac{c\;\sin\;\theta_{2}}{\tan\left( {\theta_{1} + \theta_{2}} \right)} - {\cos\;\theta_{2}}} \right)\sin\;\theta_{t}}} = 0.$This equation in θ_(t) is solved using the change of variableg=tanθ_(t)/2. Note that there are in general 2 solutions to thisequation. However, these solutions are equal modulo π, so that theydefine the same line L_(t).

The needle is rotated by angle θ_(t) from position L₃ to L_(t). Thisachieves visual servoing. At position L_(t), the needle is visuallyaligned to the target in the 2D image.

Note that only visual alignment is achieved. Unless the 3D target Tbelongs to plane Π, full 3D alignment is not achieved. As shown insection 1, complete 3D alignment can be obtained only by performingvisual servoing of the needle in several successive planes.

It should be noted that this visual servoing technique does not requireany camera calibration. It also converges in exactly three iterations,contrary to most visual servoing approaches, which require a variableand typically a larger number of iterations. This is important in X-rayapplications where each new image increases the radiation exposure ofboth patient and surgeon.

This visual servoing approach can be applied to any imaging device thatcan be approximated by a pinhole camera. In applications where thenumber of iterations is not critical, precision can be improved byconsidering n>3 successive needle positions L₁, L₂, . . . , L_(n). Thenθ_(t) can then be estimated by least-square approximation from all thepossible cross-ratios between lines L₁, L₂, . . . , L_(n).

In accordance with the present inventive concepts, combining bothapproaches (see section 1 and 2) ensures that 3D needle placement can beachieved in a fixed number (12) of iterations. This is very important asthis limits the radiation exposure of both surgeon and patient and is anadvantage of the present method over prior art methods, which usuallycannot guarantee the number of iterations that they will need toconverge.

If there are several targets to align the needle to, the alignment toall n targets can be performed in 6*(n+1) iterations, instead of 12*niterations, since some of the steps of the alignment can be used forseveral targets. The variation for orientation of a needle from a fixedpoint to multiple targets by visual servoing is the following:

It is herein assumed for the purpose of illustrative example thatimaging is provided by a simple uniplanar X-ray fluoroscope (C-arm) oranother imaging modality that can be approximated by a pinhole cameramodel. The needle itself is manipulated by a mechanical device such as apassive or active robotic arm that allows arbitrary pivoting of theneedle around its tip. The surgeon chooses a fixed needle entry point Fon the patient, and places the needle device in such a way that its tipis located at that entry point. No calibration of the set-up orregistration of the patient to the set-up is required.

The C-arm or imaging modality is then positioned, so that the targetarea and a part of the needle are both visible on the image. Thisposition corresponds to the first image plane. The surgeon defines theprojection t of the 3D anatomical target T in the image. At this pointof the description, it is assumed T remains static during the procedure.Other target points can be defined as necessary. To simplify thedescription of the approach and the figures, the case of 2 targets T andU is considered; however, this is not intended to be limiting as theapproach applies to n targets.

Let P₁ and P₂ be two arbitrary and non-parallel planes containing F (seeFIG. 3 a). For details on the choice of P₁ and P₂, see discussion below.

The mechanical device (passive mechanical arm or active robot) firstplaces the needle in plane P₁ at an arbitrary position L₁⊂P₁ (see FIG. 3b). An image is taken. 3D line L₁ projects onto 2D line l_(t) in thisimage (see FIG. 3 c). Then the needle is rotated in plane P₁ by anarbitrary angle θ₁. This brings it to position L₂, which project onto 2Dposition l₂ in a new image. The needle is again rotated, this time by anamount θ₂. This puts it into position L₃. Another image is obtained andthe corresponding 2D line l₃ is measured. The intersection point of l₁,l₂ and l₃, denoted f, is determined by least squares. Note that f is theprojection of the fixed point F around which the needle is rotated.

Let t and u be the 2D projections of the 3D targets T and U in the X-rayimage. They are given interactively by the surgeon.

Let us consider t first. The line l_(t)=(ft) is constructed. Note thatl_(t) is the 2D projection of a 3D line L_(t) in plane P₁. The rotationangle between L₃ and L_(t) is denoted θ_(t). First we calculate thecross-ratio c=(l₁, l₂, l₃, l_(t)) of the 4 intersecting 2D lines. Thiscan be done using an arbitrary line m that intersects all four lines. Ifq₁=l₁∩m, q₂=l₂∩m, q₃=l₃∩m, q_(t)=l_(t)∩m,thenc=(q ₁ q ₃ *q ₂ q _(t))÷(q ₁ q _(t) *q ₂ q ₃).

Note that the value of c is invariant to the choice of the line m. Sincecross-ratios are one of the invariants of projective geometry, we havethe following equation: (L₁, L₂, L₃, L_(t))=(l₁, l₂, l₃, l_(t))=c. Andfrom the relationship between cross-ratios and angles, we can write thefollowing formula:

$\left( {L_{1},L_{2},L_{3},L_{t}} \right) = {\frac{\left( {{\sin\left( {\theta_{1} + \theta_{2}} \right)}*{\sin\left( {\theta_{2} + \theta_{t}} \right)}} \right)}{\left( {{\sin\left( {\theta_{1} + \theta_{2} + \theta_{t}} \right)}*\sin\;\theta_{2}} \right)}.}$Therefore, we can deduce the angle θ_(t) from the value of c measured inthe image by using the following equation:

${{\left( {c - 1} \right)\sin\;\theta_{2}\cos\;\theta_{t}} + {\left( {\frac{c\;\sin\;\theta_{2}}{\tan\left( {\theta_{1} + \theta_{2}} \right)} - {\cos\;\theta_{2}}} \right)\sin\;\theta_{t}}} = 0.$There are in general 2 solutions to this equation. However, thesesolutions are equal modulo π, so that they define the same line L_(t).The needle is rotated by angle θ_(t) from position L₃ to L_(t) (see FIG.3 d). This achieves visual servoing of the needle in plane P₁, e.g. thevisual alignment of the needle and the target T. In the reminder of thispaper, L_(t) will be called D₁ ^(T) (see FIG. 3 e). Note that the 3Dalignment of the needle to T is not achieved yet.

Similarly, the line l_(u)=(fu) can be constructed and the rotation angleθ_(u) that achieves visual servoing of the needle to target U can bededuced from the cross-ratio (l₁, l₂, l₃, l_(u)). The resulting positionof the needle in plane P₁ is noted D₁ ^(U) (see FIG. 3 e). Note that thesame lines l₁, l₂, l₃ are used to achieve visual servoing in plane P₁for all the targets.

The same visual servoing procedure can be applied in plane P₂ for eachtarget. This defines 2 lines D₂ ^(T) and D₂ ^(U) belonging to plane P₂and visually aligned to the targets T and U in the image defined by thefirst position of the X-ray C-arm (see FIG. 3 e).

Let Π_(FT)=D₁ ^(T)^D₂ ^(T) be the plane defined by 3D lines D₁ ^(T) andD₂ ^(T). Since both lines project to (ft) in the image plane, this planecontains F, T and the center of the camera corresponding to the firstposition of the X-ray source. We call this plane the viewing plane oftarget T and entry point F for the first image plane (see FIG. 3 e).This is the maximum information we can get about T from a singleviewpoint. Similarly, Π_(FU)=D₁ ^(U)^D₂ ^(U) is the viewing plane oftarget U and entry point F for the first image plane.

At this point, the physician needs to move the C-arm to a second viewingdirection. The surgeon also needs to define the 2D projections t′ and u′of the 3D target points T and U in the new X-ray image.

Then we find the position of the needle in plane Π_(FT) that is visuallyaligned to target T in the new image (see FIG. 3 f). This can be done bymoving the needle first to D₁ ^(T), then to D₂ ^(T), then rotating it toa third arbitrary position and applying our cross-ratio based approachfor visual servoing of the needle in a plane (see details above). Thisresults in the complete 3D alignment of the needle, entry point F andtarget point T. The needle is then ready to insert to reach target T.The correctness of the alignment can also be checked by moving the C-armto a third viewing direction.

Similarly, the 3D orientation of the needle (FU) can be determined bymoving the needle in plane Π_(FU) and visually aligning it to target Uin the image.

Note that the complete orientation of the needle from one fixed point toone target only takes 12 iterations (or X-ray images). However, asdescribed above, if there are n targets, we do not need to do thecomplete needle orientation procedure for each target. Careful stepcounting shows that only 6*(n+1) iterations are needed to determine the3D orientations of the needle.

Note that this visual servoing technique does not require any cameracalibration. In addition and contrary to most visual servoing approachesthat usually require a variable and often large number of iterations, itconverges in a fixed number of iterations. This is important in X-rayapplications where each new image increases the radiation exposure toboth patient and surgeon.

After 3D alignment of the needle, the insertion depth required to reachthe target from the entry point can be estimated using cross-ratios. Forthis, we use markers mounted on the needle guide at known intervals. Thecross-ratio of the position of these markers, the entry point and thetarget is measured in the image. Since cross-ratios are projectiveinvariants, the 3D distance from the entry point to the target can bededuced from the cross-ratio.

Visual servoing in a plane is most precise if the plane is parallel tothe image plane. Therefore ideally P₁ and P₂ should be parallel to theimage plane. However, for a line D₁ ^(T) in plane P₁ and a line D₂ ^(T)in plane P₂ to define a plane with good precision, P₁ and P₂ shouldideally be perpendicular. The compromise we found is to useperpendicular planes P₁ and P₂ which are tilted forty-five degrees withrespect to the image plane. The error analysis simulations shown in theparagraph below seem to support this choice.

The visual servoing approach in accordance with the principles of theinvention can be applied to any imaging device that can be approximatedby a pinhole camera. In applications where the number of iterations isnot critical, the precision of visual servoing in a plane can beimproved by considering n>3 successive needle positions L₁, L₂, . . . ,L_(n). Then θ_(t) can then be estimated by least-square approximationfrom all the possible cross-ratios between lines L₁, L₂, . . . , L_(n).Similarly, if more than two positions of the imaging device are used,then the viewing planes Π_(FT) of the target T and entry point Fcorresponding to each camera pose can be intersected by least-squares inorder to determine the 3D orientation (FT). Using more camera positionsincreases precision.

The following part relating to a method for finding the best entry pointfor percutaneous procedures is distinct from the foregoing material andit applies to any imaging modality and any method for aligning a needleor linear tool to a target from a given entry point on the patient. Itcan be combined with the methods presented in section 1 and 2, orothers.

The approaches presented in previous sections supposes that the entrypoint is fixed. However, in many applications, the “optimal” entry pointmight not be known. An example of this are vertebroplasty procedures.Typically in those procedures the surgeon wants to reach a target pointinside a vertebra and wants to use a given entry point into thevertebra. However only a highly experienced surgeon is able to determinethe corresponding entry point on the skin of the patient. In thissection we propose a new method to determine the entry point necessaryfor the needle to reach an anatomical target while passing through somegiven anatomical landmark. The method (illustrated by FIG. 4) is asfollows:

Let T be the primary target and U the secondary target that the needlemust pass through. First we choose two arbitrary entry points F and G.Then we apply the technique presented in section 1,2,3 (or any othertechnique that performs the 3D alignment of a needle from an entry pointto a target using any imaging modality) to determine the 3D orientationsof the needle necessary to reach the two targets T and U from each entrypoint. This gives (FT), (FU), (GT), (GU). The intersection of the planesΠ_(FTU)=(FT)^(FU) and Π_(GTU)=(GT)^(GU) gives the direction (TU) thatpasses through both targets. The mechanical device that holds the needlecan servo the needle to this direction. By lowering the servoed needleto the skin of the patient, the surgeon can find the entry pointproposed by the system for reaching target T through target U.

In accordance with an embodiment of the invention, a primary target forbiopsy and a secondary target through which a biopsy needle must pass onits way to the primary target are given. The method for determining thebest entry point for a percutaneous procedure in accordance with theinvention comprises steps shown in FIG. 5 for the embodiment beingconsidered. The primary target T and secondary target U through whichthe needle must pass are provided at step 51. First, a first and secondarbitrary entry points on a patient are selected, at steps 52 and 53,respectively, the second point being different from the first point,followed by the following steps: determining at step 54 the threedimensional (3-D) orientation of the needle at the first arbitrary entrypoint for pointing the needle at the primary target; determining at step55 the 3-D orientation of the needle at the first arbitrary entry pointfor pointing the needle at the secondary target; determining at step 56the 3-D dimensional orientation of the needle at the second arbitraryentry point for pointing the needle at the primary target; determiningat step 54 the 3-D orientation of the needle at the second arbitraryentry point for pointing the needle at the secondary target; and, atstep 58, determining a 3-D line representing the intersection of a firstplane containing the first arbitrary entry point, the primary targetpoint, and the secondary target point, and a second plane containing thesecond arbitrary entry point, the primary target, and the secondarytarget point, whereby the 3-D line provides a position and orientationfor the needle for performing needle biopsy of the primary targetthrough the secondary target.

In accordance with another embodiment of the invention for use inconjunction with a C-arm imaging apparatus, for positioning a biopsyneedle from a given entry point on a patient to a given target forbiopsy, comprises the steps shown in FIG. 6 for this embodiment. Thesecomprise: positioning the C-arm in a desired first position, whereby animage formed with the C-arm in the first position is formed in a firstimage plane; storing location information of the given target in thefirst image plane; defining a first arbitrary plane including the givenentry point; placing the needle at the given entry point; visuallyservoing the needle in the first arbitrary plane with respect to thelocation information in the first image plane to derive a firstthree-dimensional (3-D) needle position; defining a second arbitraryplane including the given entry point, different from the firstarbitrary plane; placing the needle at the given entry point; visuallyservoing the needle in the second arbitrary plane with respect to thelocation information in the image plane to derive a secondthree-dimensional (3-D) needle position; determining a resulting planedefined by the first and second three-dimensional (3-D) needlepositions; placing the needle at a selected point in the resulting planeat an arbitrary orientation; positioning the C-arm in a desired secondposition, whereby an image formed with the C-arm in the second positionis formed in a second image plane; storing location information of thegiven target in the second image plane; and visually servoing the needlearound the entry point in the resulting plane with respect to thelocation information in the second image plane, whereby the needle is atthe entry point and aimed at the target.

In accordance with another embodiment of the invention for use inconjunction with a C-arm imaging apparatus, for visual servoing of aneedle in a plane in a fixed number of iterations, the following aregiven: a given position of the C-arm being modeled on an image plane, agiven target point for needle biopsy, a given entry point on a patient,and a given plane within which the needle can rotate around the givenentry point.

The method comprises the steps shown in FIG. 7 for this embodiment. TheC-arm position, the target point for needle biopsy, the entry point onthe patient, and the plane within which the needle can rotate areprovided at step 70. These include placing the needle in an arbitraryorientation around the given entry point at step 71, the orientationbeing associated with an angle θ1 with respect to an arbitrary referencedirection: obtain a 2-dimensional (2-D) projection image of the needlein the image plane; measure at step 72 the position 11 of the 2-Dprojection image; rotate at step 73 the needle around the entry point byan angle Δθ to a position (θ1Δθ) in the given plane; measure theposition 12 of the 2-D projection image at step 74; rotate the needlearound the entry point by an angle Δθ at step 75 to a positionθ3=(θ1+2*Δθ; measure at step 76 the position 13 of the 2-D projectionimage; locate at step 77 2-D points f and t in the 2-D projection imagethat are the respective 2-D projections of the target point and theentry point, the points f and t defining an image line It=(ft);calculate the cross-ratio c=(11, 12, 13, It) at step 78; and at step 79,determine a 3-D angle θt such that c=(θ1, θ2, θ3, θt); and rotate theneedle around the entry point by θt from position θ3 in the given plane,whereby the needle is positioned in three dimensional space at the entrypoint along a direction such that the needle is visually aligned to 2-Dprojection image of the target in the image plane.

The step of locating 2-D points f and t is performed automatically inone embodiment and manually in another embodiment.

The use and/or incorporation of computer information processing and thestorage of data is contemplated, such as the use of a programmed digitalcomputer or a dedicated computer chip or the like.

While the present invention has been described by way of illustrativeembodiments, it will be understood by one of skill in the art to whichit pertains that various changes and modifications can be made withoutdeparting from the spirit of the invention. For example, where referencein the specification and in the claims is made to a biopsy needle, itwill be understood that this may refer to a holder for such needle topermit alignment and manipulation of the needle itself as may beconvenient. Such adjunct equipment is also described in the materialsherein referenced. Such and the like modifications are intended to bewithin the scope of the invention as defined by the claims following.

1. A method for determining the best entry point for a percutaneousprocedure, given a primary target for biopsy and a secondary targetthrough which a biopsy needle must pass on its way to said primarytarget, comprising: selecting a first arbitrary entry point on apatient; selecting a second arbitrary entry point on said patient,different from said first arbitrary entry point; determining the threedimensional (3-D) orientation of said needle at said first arbitraryentry point for pointing said needle at said primary target; determiningthe 3-D orientation of said needle at said first arbitrary entry pointfor pointing said needle at said secondary target; determining the 3-Ddimensional orientation of said needle at said second arbitrary entrypoint for pointing said needle at said primary target; determining the3-D orientation of said needle at said second arbitrary entry point forpointing said needle at said secondary target; determining a 3-D linerepresenting the intersection of a first plane containing said firstarbitrary entry point, said primary target point, and said secondarytarget point, and a second plane containing said second arbitrary entrypoint, said primary target, and said secondary target point, wherebysaid 3-D line provides a position and orientation for said needle forperforming needle biopsy of said primary target through said secondarytarget.
 2. A method for determining the best entry point of a needle fora percutaneous procedure, comprising: providing a primary target T and asecondary target U through which a needle must pass on its way to saidprimary target; selecting two arbitrary entry points F and G differentfrom each other; performing a 3D alignment of said needle from eachentry point to each target to determine the 3D orientations of theneedle to reach said targets T and U from each entry point F and G, toprovide (FT), (FU), (GT), and (GU); determining a direction (TU) thatpasses through both targets from the intersection of the planesΠ_(FTU)=(FT)^(FU) and Π_(GTU)=(GT)^(GU); servoing a mechanical deviceholding the needle can servo the needle to direction (TU), wherein bylowering the servoed needle to the skin of the patient, said entry pointfor reaching target T through target U can be found.